1. Field of the Invention
The present invention relates to a core metal, an injection gear obtained by using the core metal, and a process for manufacturing a core metal, for example, the core metal for the injection gear.
2. Description of the Related Art
An injection gear is incorporated in a pinion type electrical power steering mechanism of an automobile. As illustrated in FIGS. 10A and 10B, the injection gear is molded by covering a resin gear B over the outer peripheral portion of a core metal A illustrated in FIGS. 9A and 9B. As illustrated in FIGS. 9A and 9B, Both the front and back surfaces of a peripheral portion D of a shaft hole C and an outer peripheral portion E are large in thickness. A large number of concave-convex protrusions F are formed over the entire of the outer peripheral surface of the outer peripheral portion E. The resin gear B (FIGS. 10A and 10B) molded by a molding method such as injection molding so as to cover the core metal A bites into (is locked to) the outer side of the concave-convex protrusions F, whereby slipping and displacement of the resin gear B is prevented.
A conventional core metal for an injection gear is molded by cold forging. During molding by cold forging, it is necessary to perform intermediate annealing, lubrication, and the like, thereby involving many worker-hours. Therefore, operations are continued intermittently, production time is long, and cost of metal components to be manufactured is high.